This invention relates to a method and structure for improved natural lighting for plant growth and more particularly to a method and structure for mass production of horticultural crops in environmental conditions where solar lighting under conventional conditions may be inadequate for horticultural production within a greenhouse structure.
Traditional greenhouse structures consisting of transparent panes of glass forming a roof to enclose a growing area, drawing air from the outside and having a heating system for winter months, while adequate for many purposes, possess many shortcomings which make them unsuitable for year-round production of many types of fruits and vegetables in certain climatic conditions, e.g. in climates where temperature and light conditions may be poor. Because such greenhouses often are not well sealed against the outside environment, unsuitable temperature differentials may be created within. As well, outside air which may contain substances which are not conducive to proper growth of plants, is permitted to enter. Also, exhaust products from the greenhouse heating system, which often is a natural gas or oil furnace may be present in the environment within such greenhouses again causing reduced plant growth. The water which is used in such greenhouses is often local water and again may contain impurities or compositions which impede plant growth. There is an increasing awareness of the detrimental impact of impurities in the air or water on plant growth. In addition, the concentration of elements for plant growth such as calcium, nitrogen and phosphorous in water being fed to plants in conventional greenhouses may change from day-to-day, resulting in irregular plant growth.
As a result, in recent years there has been a trend towards development of controlled environment horticultural or agricultural installations. For example, Canadian Patent No. 1,097,075 of Miller issued Mar. 10, 1981 describes and illustrates a nutrient supply system for such a controlled environment agricultural installation incorporating nutrient film techniques in which plant root masses are arranged to be wetted by contact with a small stream of liquid nutrient. Capillary attraction or wicking then is relied upon to extend the nutrient-wetted area over and through the entire root mass. Nutrient supply is achieved by positioning the plant roots in long troughs and flowing a thin stream of liquid nutrient along the bottom of the trough permitting the stream to contact each of the plant root masses as it flows along. Excess nutrient is recycled usually after any needed replenishment of its compositional elements.
Such attempts to control in a greenhouse the various conditions responsible for plant growth have heretofore been extremely limited in scope. Thus, for example, in Miller Canadian Patent No. 1,097,075, only the nutrient feed is controlled. In Canadian Patent No. 982,426 of Delano et al issued Jan. 27, 1976, a method of controlling the amount of solar heat and light which enters a glass or plastic greenhouse is described wherein a liquid is coated on the glass or plastic film of the greenhouse. The liquid dries into a coating which is transparent under certain conditions and non-transparent under other conditions. In Canadian Patent No. 955,748 of Glatti et al. issued Oct. 8, 1984, the light passing through a translucent covering of a greenhouse is partially controlled by coating the inner surface of the translucent covering with a surface-active agent, which surface-active agent reduces the contact angle of water-condensate droplets formed on the inner surface thereof to below 75.degree..
Other patents of general background interest describing different types of greenhouse structures include U.S. Pat. No. 4,195,441 of Baldwin issued Apr. 1, 1980 (solar greenhouse in which plants are used as solar collectors to absorb solar radiation and store it in a heat reservoir beneath the greenhouse) and U.S. Pat. No. 4,352,256 of Kranz issued Oct. 5, 1982 (greenhouse structure including a central hub and arms comprising growth chambers extending radially outwardly therefrom).
While previous attempts to provide controlled environment horticultural installations have apparently been successful for the limited purposes for which they were developed, such structures have not really addressed the difficulties of producing horticultural crops in any quantity using natural lighting at latitudes where solar angles are very low, e.g. during winter months. Thus, for example, even with a properly maintained greenhouse installation, during winter months the solar angle may be so low that little or no fruit or vegetable production can be achieved in plants within the greenhouse. Thus, for example in Canada and the Northern United States, during the middle winter months when the solar angle is lowest, plants such as tomatoes and cucumbers will not produce vegetables. As well the growth rates of such plants are significantly reduced as compared to their growth rates during the summer months when the solar angle is greatest. Hence, up till now, it has been virtually impossible to go into large scale production of fruit and vegetables in such regions, during the winter months, and virtually all of the fresh fruits and vegetables to be consumed persons inhabiting such regions during the winter months have had to be imported from more temperate regions where the solar angle is higher and fresh fruits and vegetables can be produced either in greenhouse or outdoor conditions.
Thus, it is an object of the present invention to provide a structure and method for improved natural lighting for plant growth which will permit large scale production of horticultural crops even in conditions of relatively low solar angle such as those experienced in Northern United States or Southern Canadian areas during the winter months.